There are many applications where it is desirable to extend the effective length of a tool. Increasing the lever arm of a tool increases the mechanical advantage of the tool. As one example, a crowbar with a long lever arm is useful for prying apart strongly coupled pieces of wood or metal. As another example, it is desirable to have a long lever arm on a vertical car-jack in order to increase the mechanical advantage such that a heavy car can be jacked up with normal arm strength.
Mechanics often desire to increase the effective length of a wrench. This increases the mechanical lever arm of the wrench, thereby permitting greater torque to be applied to a nut. This is particularly desirable if the nut which is to be loosed is frozen or otherwise requires a large torque in order for it to be removed. For example, head bolts in diesel engines are typically tightened to 500 ft-lbs of torque. Consequently, a wrench with a long effective lever arm is desirable to break such nuts loose. There are also other applications where it is difficult with common wrenches to apply sufficient torque to a nut. For example, many wrenches used for common nut sizes, such as 3/8" wrenches, are commonly available in lengths substantially less than one foot in length (e.g., six to ten inches). The short lever arm of such wrenches makes it difficult for professional mechanics to apply sufficient torque to crack tight nuts. Furthermore, a short lever arm may make it impossible for many home mechanics with limited strength (e.g., the elderly and the disabled) to apply sufficient torque to loosen frozen nuts.
There are also other applications where it is desirable to increase the effective handle length of a wrench. In particular, increasing the effective handle length of a wrench is often desirable in applications when a mechanic must tighten and/or loosen nuts in a compact, restricted space, such as in an automobile engine. Mechanics often have "short handled" and "long handled" versions of common wrenches in order to increase their cap to grasp the tool in a "clear area" while applying torque to a nut in a recessed or constrained area. However, for economical and practical reasons conventional wrenches typically come in only a limited range of lengths (e.g., conventional 3/8" wrenches typically have handle lengths substantially less than one foot in length) such that conventional wrenches are often not of a convenient length to be used to tighten and/or loosen nuts in a restricted space.
One technique that mechanics commonly use to surmount the limitations of the limited handle length of common wrenches is to insert the opposite end of the wrench into a length of cylindrical pipe, thereby increasing the effective handle length of the wrench. Such a pipe-extension permits a mechanic to greatly increase the lever arm of common wrenches, and thus apply a substantial torque to a nut. However, using a pipe extension has many drawbacks. For example, inserting one end of a 3/8" wrench into a two-foot long piece of pipe with an inner diameter slightly larger than the cross sectional width of the end of the wrench more than doubles the lever arm of a conventional 3/8" wrench having a handle that is less than one foot in length. One problem is that the wrench may slip in the pipe during its use so as to cause the nut to be stripped. Another problem is that a pipe extension can be a safety hazard. At high torque levels, a wrench that slips in a pipe extension may cause the wrench to fly off of the nut. Automobile mechanics often bruise their knuckles when such pipe-extensions slip during use. There are also some high-torque applications where a wrench may be thrown with substantial momentum if the pipe extension slips during use. For example, mechanics sometimes use a pipe extension to increase the lever arm of pipe wrenches. However, a pipe extension may slip, particularly if a mechanic attempts to tighten overhead pipes. Consequently, the pipe wrench may be thrown and/or fall onto the mechanic.
The inventor of the present invention believes that mechanics continue to use pipe-extensions as a means to increase the length of their wrenches because previously known wrench extension handles do not adequately solve the problems of providing an economical extension handle that can be used with a wide variety of wrench sizes and which provides a secure grip on a wrench at high torque. Previously known wrench extension handles, such as that described in U.S. Pat. No. 1,511,738, commonly use two oppositely positioned stirrups to receive the wrench handle near one end of the extension handle. The stirrups are typically substantially U-shaped holders spaced apart a short distance on one end of an extension bar. The wrench is held by the slots formed by the two U-shaped holders, thereby increasing the effective lever arm of the wrench. However, unless the wrench handle has a thickness substantially the same as that of the slot width of the U-shaped holders, there may be excessive "play" between the wrench handle and the U-shaped holders. Even a very small amount of play between a U-shaped holder and a wrench handle may be unacceptable at high torque levels. These problems tend to limit conventional wrench extension handles to use with a narrow range of wrench sizes (e.g., wrenches with a handle thickness and width comparable to the U-shaped holders) and to comparatively low torque levels.
There are other limitations to the wide-scale use of previously known wrench extension handles. Previously known extension handles are commonly designed such that only a small portion of the wrench (e.g., the open or box end) may extend out from the extension handle. This facilitates the mechanical coupling of the wrench to the extension handle and helps to reduce the play of the wrench. However, it is highly undesirable because mechanics typically require a wide range of effective handle lengths. As previously described, a mechanic often needs to extend a wrench to provide greater accessability to nuts which are located in a constrained area. The effective wrench length may be defined as the total length of the wrench as placed in the extension handle. In some applications, there may only be a limited "window" of effective wrench lengths for which the mechanic may firmly grasp the extension handle while still being able to turn the extension handle. Consequently, previously known extension handles may not be suitable for use in constrained spaces because the effective wrench length is not selectable.
Another limitation of previously known wrench extension handles is that they do not accommodate a range of wrench shapes. A mechanic often uses wrenches with angled box-ends in addition to flat open-ended wrenches. Box-end wrenches typically have a box end angled at thirty degrees, although box-end wrenches with a box end angled at forty-five degrees are also commonly used. The angled box-ends make it difficult to design U-shaped holders which provide a strong mechanical coupling to the wrench. One attempted solution, as described in U.S. Pat. No. 4,960,014, is to elevate the U-shaped holders relative to the rest of the extension handle such that the U-shaped holders will couple to the flat handle portions of the curved wrench. However, elevating the U-shaped holders raises the body of the wrench above the extension handle such that at most one point on the back end of the curved wrench contacts the handle. This makes a precise matching of the size of the wrench (e.g., wrench thickness, width, and length) to the U-shaped holders more difficult to achieve to avoid play, particularly if the extension handle is cocked at a slight angle with respect to the nut.
The ideal extension handle for wrenches would provide a firm coupling to a wrench even at extremely high torque levels. The extension handle would also maintain a firm coupling even if the extension handle was slightly tilted with respect to the plane of the nut. Additionally, the ideal extension handle would be compatible with a wide range of wrench handle thicknesses, widths, lengths, and curvature such that a mechanic could use a small number of extension handles to extend a large number of different wrench sizes and types. Moreover, the ideal extension handle would permit a mechanic the capability to conveniently adjust the effective length of his wrench to facilitate using the extended wrench in constrained spaces, thus eliminating the need to have a large variety of extension handle lengths. Unfortunately, no previously known extension handle for wrenches provides a practical means to achieve these objectives.
What is desired is an extension handle suitable for a wide range of wrench types and dimensions that permits a wrench to be adjustably extended from the extension handle and which firmly holds the wrench in place during use even at high torque levels.